import type { ObjMap } from './ObjMap';

/**
 * Creates a keyed JS object from an array, given a function to produce the keys
 * and a function to produce the values from each item in the array.
 * ```ts
 * const phoneBook = [
 *   { name: 'Jon', num: '555-1234' },
 *   { name: 'Jenny', num: '867-5309' }
 * ]
 *
 * // { Jon: '555-1234', Jenny: '867-5309' }
 * const phonesByName = keyValMap(
 *   phoneBook,
 *   entry => entry.name,
 *   entry => entry.num
 * )
 * ```
 */
export function keyValMap<T, V>(
  list: ReadonlyArray<T>,
  keyFn: (item: T) => string,
  valFn: (item: T) => V,
): ObjMap<V> {
  const result = Object.create(null);
  for (const item of list) {
    result[keyFn(item)] = valFn(item);
  }
  return result;
}
